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Water Scarcity

All but the most desert-adapted mammals require free water for their survival. Bats are particularly susceptible to physiological water stress due to their large body surface to volume ratio and water loss through their wing membranes.

Research has documented bats losing up to 30% of their body weight in a 12 hour period due to evaporative water loss. Insectivorous bats - which comprise almost 75% of the 1,300+ known bat species and 44 of the 47 species in the U.S. and Canada--are especially susceptible as they receive less metabolic water from their food than bats that feed on fruit or nectar. Pregnant and lactating bats, a key demographic to maintaining population levels, experience the highest levels of water stress.

Because bats drink while in flight, they can only drink from water sources that are unobstructed and pooled or slow-moving, further restricting the availability of suitable drinking sites. In arid and semi-arid regions, the availability of water and its associated riparian foraging habitat can have pronounced effects on bat abundance, distribution, diversity, community structure, and habitat use. Long-term research on insectivorous bats in the western U.S. found reproductive fitness declined significantly with diminishing surface water.

The distribution and abundance of natural water sources in the West has decreased dramatically over the past century, even before the threat of changing climate, due primarily to expanding human settlement and associated natural resource uses such as turn of the century overgrazing, irrigation agriculture, and urban and exurban development. Bats are opportunistic, and while natural water sources have disappeared, bats will also drink from human-made water sources. In much of the West, bats now rely on water sources developed for livestock such as troughs and stock ponds, and they’ll also drink from constructed waters such as reservoirs, settling ponds, swimming pools, and other impoundments. Natural water sources however have additional value to bats due to their accompanying riparian (water associated) habitat, a high-quality foraging habitat not often associated with constructed waters.

Unfortunately, the abundance, distribution, and availability of all water sources, both natural and constructed, are all decreasing due to the effects of changing climate and competing resource uses. According to the International Panel on Climate Change, the western U.S., and the Southwest in particular, have experienced 70% more warming than the average global increase for the 20th century, and this warming has been linked to changing precipitation patterns, including precipitation intensity and extremes and changes in soil moisture and runoff (i.e. surface water). The quantity of rainfall has decreased over the last century in the western U.S., and the climate models for the 21st century are consistent in projecting a continuing decrease in precipitation, river runoff, and water availability. If accurate, these trends portend severe impacts to regional bat populations.

North American Areas of Intersecting Water Stress & Bat Species Diversity

BCI is working on climate adaptation measures that will increase the distribution and quantity of clean, accessible, and reliable water and associated riparian habitat for bats in the face of changing climate through a combination of outreach, capacity building, and on the ground conservation. Over the last decade, BCI’s Water for Wildlife Program has worked with dozens of private and public forest and range managers across the west to ensure that tens of thousands of livestock water developments, now an essential water source for western bats, provide safe and accessible water for bats.

BCI has also trained hundreds of western natural resource managers in techniques for restoring and creating wetland and pooled water drinking and foraging habitat for bats, and has collaborated with dozens of agencies and organizations to actively create or restore water resources at dozens of the most species rich and water-limited sites in the West. BCI’s new Public Lands Program will expand these efforts and ensure that the conservation of bat populations and water resources are incorporated into federal natural resource management policy and planning on the more than 600 million acres of public forest, desert, and rangelands across the West.